If briefly

Reverse osmosis is a regular membrane, or more precisely, a thin film with very tiny openings.
It allows water to be separated, making it 99% pure.
In fact, it is a process of separating water into clean and residual.

Unlike a simple filter, where particles remain inside it.

More in detail

Imagine a bag, but long, and it is wound around a tube with holes.
One side of the bag is solid film, and the other has very tiny openings, the size of a water molecule.
When water under pressure passes between the layers — water molecules penetrate into the bag, while bacteria and other residues, slightly larger, continue further (to the other side, to the outlet).
Inside the bag, there is a mesh so that clean water can freely pass to the center of the tube.

Thus, it is more like separation of clean water from dirty water.
But in nature, this process was called reverse osmosis, even though there is nothing “reverse” about it.

Why specifically separate clean from dirty

Because the purification process in this way, although it gives a good result, has a small drawback — it is impossible to separate all the water, otherwise the membrane would just clog.

About half of the water becomes clean, and the other half goes to the drain.

How much water goes to the drain

In good filters, this ratio is 1:1, meaning for 1 liter of clean water, 1 liter of dirty water is discarded.
Actual figures can vary from 1 to 8 liters, depending on the brand and usage time.

Moving on

So, the membrane (filter) consists of a special bag (of course, made of food-grade film), wound around a tube with holes, which serves as the distributor.

When the filter (membrane) is inserted into the housing, water is fed onto it from above under pressure. After passing the separation, it reaches the bottom of the housing.
Clean water exits through a tube to a separate outlet.
The residues, passing between the layers, exit the bottom of the housing through another opening.

Why other filters are needed in a reverse osmosis system

If the water is not pre-treated before the osmotic membrane, it clogs quickly.

The first filter at 5–10 microns removes rust, silt, etc.
The second filter (usually carbon) softens water and kills microbes.
The third filter at 1 micron (not very critical, but desirable) removes residues and any particles from the carbon filter.

After these filters, the water is already much cleaner.
But scale (salts, minerals), some microbes, and heavy metals are still in the water.
Then the osmotic membrane comes into play, where only clean water (99%) is separated.

How true is it, and how well does it clean

Immediately, I’ll say — yes. It cleans well, practically pure H2O without impurities.
The osmotic membrane (film) passes only water molecules and sometimes only 1% of very tiny particles.
Everything else, as waste, goes further to the drain.
Thus, the membrane self-cleans.
But there is a nuance — this is practically not beneficial water, as it does not carry minerals necessary for humans.
Therefore, after osmosis, a mineralizer is installed.

Now let’s look at how everything works in general

Tap water flows through pre-filters.
5–10 micron, carbon, 1 micron
A valve regulates the pressure at the drain outlet.
Pressure is needed to “push” the water into the membrane, otherwise it would simply flow into the drain.
The membrane itself separates water into clean and residual.
Residual water goes to the flow restrictor (maintains correct pressure) and into the drain.
Purified (distilled) water goes to the mineralizer, is enriched with beneficial minerals and salts.
It reaches the consumer’s tap.

Why mineralization is needed

Water itself — pure H2O — contains nothing beneficial.
Our body needs minerals and salts daily.
Even crystal-clear spring water is H2O with minerals and salts.

Tap water, passing through pipes and disinfection, becomes more saturated with minerals and salts, making it less beneficial — this is scale in a kettle and kidney stones.

To balance minerals, first, reverse osmosis removes everything from the water.
Then, after osmosis, the mineralizer enriches the water with the necessary minerals and salts in the required amount.

Interesting questions

Can we do without osmosis and a mineralizer?
Of course, we can, but a filter that reduces “scale” would be significantly more expensive.
So it is more efficient to remove everything and add what is needed.

Does the membrane clog?
Yes, over time (half a year, a year), depending on water quality and usage.
Although the membrane self-cleans, some silt gradually settles.

Can the membrane be washed?
Yes, but it is not guaranteed that it can be fully restored.
However, it is possible to flush it by running water from the drain side (in reverse order), temporarily switching the tubes.

Interesting facts

In plants, osmosis helps cells absorb water from the soil. If the salt concentration in the soil is lower than inside the cell, water moves into the cell, maintaining turgor and shape.

In the human body, osmosis is important for maintaining fluid balance in cells and tissues. For example, kidneys regulate the concentration of water and salts in the blood through osmotic processes.

Types of osmosis

Direct osmosis — water moves from a less concentrated solution to a more concentrated one through a membrane.

Reverse osmosis — water moves against the natural concentration gradient under pressure. It is used in water purification and seawater desalination systems.

Where osmosis is used

Water filtration: reverse osmosis systems remove salts, bacteria, and other impurities from drinking water.
Food industry: osmosis is used to concentrate fruit juices and dairy products.
Medicine: infusion solutions must have osmotic pressure compatible with blood to avoid cell damage.

Osmosis is extremely important in biology, medicine, and industry, allowing control of fluid balance and water purification.